The present invention relates to medical devices in general, and in particular to atherectomy devices for removing occluding material from a patient""s blood vessels.
Vascular diseases, such as arteriosclerosis and the like, have become quite prevalent in modern day. These diseases may manifest themselves in a number of ways, often requiring different forms or methods of treatment for curing the adverse effects of the diseases. For example, vascular diseases may take the form of deposits or growths in a patient""s vasculature which may restrict, in the case of a partial occlusion, or, stop, in the case of a total occlusion, blood flow to a certain portion of the patient""s body. This can be particularly serious if, for example, such an occlusion occurs in a portion of the vasculature that supplies vital organs with blood or other necessary fluids.
To treat these diseases, a number of different invasive and minimally invasive therapies have been developed. For example, cardiac bypass surgery is now a commonly performed procedure whereby an occluded cardiac artery is bypassed with a segment of a healthy blood vessel that is obtained from elsewhere in the body. While this procedure is generally successful, it is fairly traumatic because the entire chest cavity of the patient must be opened to access the occluded vessel. Therefore, the procedure is generally not performed on frail or elderly patients.
As an alternative to bypass surgery, it is also fairly common to treat occluded vessels using an intravascular device. Such treatment devices, sometimes referred to as atherectomy or ablation devices, use a variety of material removal means, such as rotating cutters or ablaters, to remove the occluding material. The material removal means, such as a rotatable burr, is typically coupled to an electric motor or air turbine via a drive shaft that extends out of the patient""s body. The drive shaft is rotated and the burr is advanced through the occluding vessel. The rotating burr grinds the occluding material into sufficiently small fragments that are removed by the body, rather than merely displacing or reforming the material in the vessel as in a balloon angioplasty procedure.
One problem faced by physicians when performing an atherectomy procedure is determining if all of the stenosis has been ablated by the ablation burr while the ablation burr is within the occluded area. While imaging techniques such as fluoroscopy or external ultrasound have been developed to image a person""s vasculature, these techniques generally cannot resolve a thin layer of occluding material that remains on a vessel wall. Therefore, there is a need for an atherectomy device that can image the interior of a patient""s vasculature without removing the ablation burr from the occluded site.
Yet another problem that occurs with conventional atherectomy devices is the fact that they can only create lumens of a fixed size. Therefore, if a physician wants to increase the size of a lumen, the driveshaft and burr have to be removed from the patient and replaced with a larger diameter burr. Therefore, there is a need for an atherectomy device that can create various sized lumens with a single burr.
Another area for improvement of conventional atherectomy devices is with the driveshaft. As indicated above, rotational energy is transferred from the motor or turbine to the ablation burr with a drive shaft. Most drive shafts are constructed of wound steel. For example, a Rotoblator(copyright) atherectomy device as developed by Boston Scientific uses a wound steel coil to transmit the rotational energy created outside of the patient""s body to the burr located within a blood vessel lumen or other body channel. Currently, in order to provide sufficient torque carrying capacity, flexibility, and strength the drive shaft is constructed of three steel wires, each of which is 0.006 inches in diameter, that are wound into a coil configuration.
Drive shaft flexibility affects how the drive shaft is controlled and performs in the patient. While a stiff drive shaft is easily advanced through vasculature, it may not easily conform to the vasculature. A drive shaft that is too flexible, however, may stall as it is being advanced. Additionally, a drive shaft having rough edges may not advance smoothly through the stenosis being ablated. For example, tissue could possibly become trapped within the coils of the drive shaft thereby restricting movement of the drive shaft and adversely affecting control. Therefore, it is desirable to improve the drive shaft to be smaller, more flexible and smoother than currently available drive shafts.
An atherectomy device according to the present invention allows images of an interior vessel wall to be obtained as ablation is occurring in order to ensure that substantially all occluding material is removed from a vessel during an ablation procedure. In one embodiment of the invention, an atherectomy device includes an integrated imaging sensor such as an intravascular ultrasonic transducer. The transducer is preferably disposed on the distal end of a guide wire. The guide wire is routed through a separate lumen of a guide catheter in which an ablation device is routed.
In accordance with another aspect of the present invention, the atherectomy device includes an expandable distal end that forces an ablation burr against a vessel wall such that a single device can be used to create various sized lumens in a patient""s vasculature.
In accordance with another aspect of the present invention, the diameter of a lumen that can be created in the vessel is continuously variable by routing the ablation device through a control shaft having a predefined bend at its distal end. The bend in the control shaft is extended from or drawn into a lumen of a surrounding guide catheter. The bend in the control shaft displaces an ablation burr laterally in a vessel depending upon the amount of the bend that extends distally from the end of the surrounding guide catheter. To create a lumen in a vessel, the control shaft is rotated within the surrounding guide catheter.
In accordance with another aspect of the invention, a drive shaft that rotates an ablation burr is made of a lightweight polymeric material such as a liquid crystal polymer. Fibers of the liquid crystal polymer are braided or wound to optimize the torque or flexibility aspects of the drive shaft as needed.